For vehicle interiors, housings of household electric and electronic appliances and also housings of compact mobile devices, a decorative molded body in which a decorative film including a design layer is integrated with a resin molded body is widely used. The integral decorative molded body is produced by attaching a resin molded body to the design layer of the decorative film. The decorative molded body thus obtained has an external appearance which causes a viewer to perceive that the molded body has a certain depth. Such a decorative molded body also has an advantage that the decorative layer is not deteriorated due to abrasion even after being used for a long time.
According to one exemplary method for integrating the resin molded body and the decorative film, the decorative film is inserted into a mold for injection molding without being preliminarily molded, and a melted resin is injected into the mold, so that an injection-molded body is formed and at the same time, the decorative film is bonded to the molded body. According to another exemplary method for integrating the resin molded body and the decorative film, the decorative film is preliminarily molded by thermoforming (vacuum forming, air-pressure forming, vacuum-pressure forming, etc.) and set in a mold for injection molding, and a melted resin is injected into the mold, so that an injection-molded body is formed and at the same time, the molded body is integrated with the preliminarily molded decorative film.
A transparent sheet to be subjected to printing that is used for forming a decorative film may be, for example, a polycarbonate single-layer sheet or an acrylic resin single-layer sheet. The polycarbonate single-layer sheet has high toughness and high flexibility but has a problem of having low surface hardness and thus allowing the surface of the molded body to be scratched easily.
Although polycarbonate is not highly evaluated as a material for a decorative film, the following methods, for example, are available to increase the surface hardness of a polycarbonate molded body: a method of using polycarbonate having a specific structural unit (Patent Document 1); and a method of using a resin composition formed of polycarbonate and a specific (meth)acrylate copolymer (Patent Document 2).
By contrast, the acrylic resin single-layer film has high surface hardness and thus high scratch resistance but has low toughness and low flexibility. Therefore, the acrylic resin single-layer film has problems of being difficult to be formed and being damaged, for example, broken while being handled or transported.
As a film that alleviates these problems, a film containing acrylic rubber particles incorporated into the acrylic resin and thus having an increased flexibility has been proposed (Patent Document 3).
As a film having both of high flexibility and high surface hardness, a laminate film of acrylic resin and polycarbonate has been proposed (Patent Document 4). Such a laminate film has a molded body surface of acrylic resin and a printing surface of polycarbonate, and thus has toughness and flexibility higher than or equal to those of the acrylic resin single-layer film while maintaining the surface hardness of the acrylic resin.
However, such multi-layer films may have a molding flaw such as whitening, cracking, foaming or the like caused at the time of molding due to the high thermoforming temperature. This significantly narrows the molding conditions. In addition, in order to maintain the hardness of the film, the acrylic resin layer needs to have a certain thickness. Therefore, as the total thickness of the film is smaller, the ratio of the thickness of the acrylic resin layer with respect to the total thickness is higher. This significantly decreases the toughness and the flexibility of the film. Furthermore, when the hard-coated film is to be molded by thermoforming, the processing temperature needs to be the processing temperature for polycarbonate. This causes conspicuous whitening, cracking, foaming or the like to the hard-coat on the acrylic resin layer.
For lowering the thermoforming temperature, the following methods are available: a method of using a polycarbonate resin composition having a lower deflection temperature under load (ISO75, load of 1.8 MPa) for a laminate sheet of acrylic resin and polycarbonate (Patent Document 5); and a method of performing polymer alloying of a polycarbonate resin layer and a different resin (aromatic polyester) to lower the glass transition temperature (Tg) of the polycarbonate resin layer and thus to lower the molding temperature (Patent Document 6). However, in such multi-layer sheets also, the acrylic resin layer needs to have a certain thickness in order to maintain the surface hardness. Therefore, as the total thickness of the film is smaller, the ratio of the thickness of the acrylic resin layer with respect to the total thickness is higher. This significantly decreases the toughness and the flexibility of the film. In addition, the above-described documents do not describe a laminate resin sheet including a hard-coat layer provided on a surface of the acrylic resin layer.